Hydraulic machine

ABSTRACT

The invention concerns a hydraulic machine with a set of teeth, having a toothed ring with an inner toothing and a gear wheel with an outer toothing, the gear wheel rotating and orbiting in the toothed ring, the inner toothing and the outer toothing touching each other in contact areas, thus separating pressure chambers, and with a valve arrangement controlling a connection between a connection arrangement having a high pressure connection and a low pressure connection, and the pressure chambers. It is endeavoured to achieve a stable operation, particularly with low speeds. For this purpose, each contact area is provided with an opening, which, at the time when a pressure chamber reaches an extreme value of its volume, produces a short-circuiting with the neighbouring pressure chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in InternationalApplication No. PCT/DK03/00124 filed on Feb. 27, 2003 and German PatentApplication No. 10209672.4 filed on Mar. 5, 2002.

FIELD OF THE INVENTION

The present invention concerns a hydraulic machine with a set of teeth,having a toothed ring with an inner toothing and a gear wheel with anouter toothing, the gear wheel rotating and orbiting in the toothedring, the inner toothing and the outer toothing touching each other incontact areas, thus separating pressure chambers, and with a valvearrangement controlling a connection between a connection arrangementhaving a high pressure connection and a low pressure connection, and thepressure chambers.

BACKGROUND OF THE INVENTION

A hydraulic machine of this kind is, for example, known from EP 0 959248 A2. During motor operation, the valve arrangement supplies theexpanding pressure chambers with pressurised hydraulic fluid from thehydraulic connection, whereas the contracting chambers are connectedwith the low-pressure connection via the valve arrangement, so that thehydraulic fluid from the contracting pressure chambers can be displaced.When the machine is operated as a pump, the valve arrangement connectsthe contracting pressure chambers with the high-pressure connection andthe expanding chambers with the low-pressure connection.

In such machines, it is important that the supply to the individualpressure chambers is controlled relatively accurately by the valvearrangement. This is particularly crucial, when a transition from anexpansion phase to a contraction phase occurs in a pressure chamber,that is, when the pressure chamber has reached its maximum volume or itsminimum volume.

The known machine has a secondary commutation, which ensures that anypressure chamber has a connection outside the valve arrangement to anyneighbouring pressure chambers until shortly before it reaches a minimumor a maximum volume. At the instant of the commutation it is ensuredthat there is no connection between the pressure chamber with maximum orminimum volume and the corresponding neighbouring pressure chambers.Thus, a stable operation with low speeds and high pressures is achieved.

A hydraulic machine as mentioned in the introduction, which is alsocalled a gerotor machine, drives a valve element of the valvearrangement, which influences the correct positioning of the supply ofthe pressure chambers, via a cardan shaft or via another couplingarrangement. For several reasons, this may cause a small angledisplacement between the valve element and the gear wheel that drivesthe valve element. Under certain circumstances, this angle displacementmay cause that the pressure chambers are not connected with thecorresponding supply connections in the correct position. This causes aninstable operation, and in the extreme it may even lead to a damaging ofthe machine.

The invention is based on the task of achieving a stable operation,particularly with low speeds under high loads.

SUMMARY OF THE INVENTION

In a hydraulic machine of the kind mentioned in the introduction, thistask is solved in that each contact area is provided with an opening,which, at the time when a pressure chamber reaches an extreme value ofits volume, produces a short-circuiting with the neighbouring pressurechamber.

Thus, a second commutation is achieved, which ensures that impermissiblepressure peaks in the pressure chambers can be avoided. Avoiding thepressure peaks is independent of whether or not the valve arrangementdoes actually ensure that the supply of the pressure chambers takesplace in the correct position. Of course, also the control of the valvearrangement has certain limits, which cannot be exceeded. On transitionfrom an expansion phase to a contraction phase or vice versa, theopening ensures that also with a slightly incorrect control by the valvearrangement a pressure equalisation can take place between neighbouringpressure chambers. This will cause a short-circuiting between thehigh-pressure side and the low-pressure side. Until now, it has alwaysbeen endeavoured to avoid such a short-circuiting. As, however, thisshort-circuiting is only exposed to the highest pressure difference fora relatively short period, and as it is possible to have a certaininfluence on the amount of penetrating fluid by means of the size of theopening, the damaging effects of such a short-circuiting are extremelysmall. The positive effects achieved by the pressure equalisationcompletely neutralise these damaging effects.

It is particularly preferred that the opening is a throttle opening.Thus, the “loss” of hydraulic fluid flowing through the throttle openingcan be kept small. This causes an increase of the volumetric efficiency.

Preferably, the throttle opening has a variable throttling resistance,which is largest at the moment, when the pressure chamber has an extremevalue of its volume. This gives a gradual throttling of the fluid flowbetween neighbouring pressure chambers until the time, when one of thetwo pressure chambers assumes its maximum or its minimum volume. Thus,an additional pressure surge is avoided, which could occur, whensuddenly a throttle was inserted in this fluid path. Anyway, the fluidloss at the moment of commutation is kept small.

Preferably, the opening is formed by a recess in a tooth side. This is arelatively easy way of producing such an opening. A recess is easilymade, for example by milling.

Preferably, the recess is made in the outer toothing. The outer toothingis often made by means of a moulding of the gear wheel, whereas theteeth of the inner toothing of the toothed ring are often in the shapeof rollers, which can rotate in the toothed ring. When the recess ismade in the outer toothing, it has a fixed position, which does notchange in relation to the toothing geometry.

Preferably, the recess has a plane or concavely arched bottom. A recessof this kind is easily made, for example by milling. A plane bottom ismade by a milling cutter. Depending on the diameter of the disc, aside-milling cutter can, under certain circumstances, produce aconcavely arched bottom. As the remaining tooth side is arched, thiswill result in a gradually increasing depth of the recess. This is asimple way of achieving a variable throttle resistance, which reachesits highest value, when the pressure chamber in question has reached itsmaximum or its minimum volume.

Preferably, the recess is arranged in the axial centre of the toothing.Thus, possibly occurring asymmetric forces on the toothed set can beavoided. In the axial direction, the recess is relatively short.Accordingly, enough space for arranging the recess is available in theaxial centre of the toothing.

Preferably, a recess is arranged on either side of a tooth. Thus, themachine can be driven independently of the rotation direction. In allcases, it is ensured that, when reaching the minimum volume or themaximum volume of a pressure chamber, a connection to the neighbouringpressure chamber exists, through which a pressure can be built up.

Preferably, the valve arrangement has a rotatably driven valve plate,which is supported in a substantially plane manner on a channel plate.Compared with a drum slide valve, a plane slide valve of this kind hasthe advantage that it can work with a smaller play, thus having animproved tightness. However, it must be ensured that during operationthe balance of the valve plate is as good as possible, to avoid a tooheavy wear caused by friction in relation to the channel plate.

It is preferred that the valve plate is loaded in the direction of thechannel plate by a spring-biased balancing plate. The spring biasingensures the sealing between the valve plate and the channel plate duringstart-up. Later, the force in the direction of the channel plate isensured by the oil pressure, which builds up inside the machine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described in detail on the basis of apreferred embodiment in connection with the drawings, showing:

FIG. 1 is a longitudinal section through a hydraulic machine

FIG. 2 is a section II-II according to FIG. 1

FIG. 3 is a perspective view of a gear wheel

FIG. 4 is a cross-section IV-IV according to FIG. 1 in one position ofthe gear wheel

FIG. 5 is an enlarged section V of FIG. 4

FIG. 6 is a view according to FIG. 4 with another position of the gearwheel

FIG. 7 shows an enlarged section VII according to FIG. 6

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A machine shown in FIG. 1 is in the form of a motor 1, which has anoutput shaft 2. The output shaft 2 is driven by a gear wheel 3, whichhas an outer toothing 4 an rotates and orbits in a toothed ring 5, whichhas an inner toothing 6 in the shape of rollers 7. The output shaft 2 isconnected with the gear wheel 3 via a cardan shaft 8, which is insertedinto a suitable toothing 9 in the inside of the gear wheel 3.

On the side facing away from the cardan shaft 8, the toothed setconsisting of the gear wheel 3 and the toothed ring 5 is covered by acover plate 10. On the opposite side, the toothed set is covered by achannel plate 11, which cooperates with a valve plate 12. The valveplate 12 engages with an extension 13 of the output shaft 2, so that thevalve plate 12 rotates synchronously with and at a predetermined anglerelation to the gear wheel 3.

Together, the channel plate 11 and the valve plate 12 form a valvearrangement, which controls the supply from a connection arrangement 15of the pressure chambers 14, which are formed between gear wheel andtoothed ring 5 (FIG. 2), only one connection of the connectionarrangement 15 being visible in FIG. 1. The connection arrangement 15has a high-pressure connection, at which pressurised hydraulic fluid issupplied into the motor, and a low-pressure connection, through whichthe hydraulic fluid can flow off from the motor.

In order to ensure the tightness between the valve plate 12 and thechannel plate 11, a balancing plate 16 is provided, which is arranged onthe side of the valve plate 12 facing the channel plate 11. This ensuresthe corresponding tightness between the channel plate 11 and the valveplate 12 during start-up. Later, the required force on the valve plate12 is provided by a pressure in a pressure chamber 18, in which acorresponding oil pressure builds up during operation of the motor.

The cardan shaft 8 is connected with the output shaft 2 by means of anadditional toothing 19. Neither with the toothing 9 nor with thetoothing 19 a play can be completely avoided. Particularly in connectionwith high loads, it is further possible that the cardan shaft 8 getstwisted. The sum of these occurrences now contribute to the fact thatthe supply in the correct position of the individual pressure chambers14 between the toothed ring 5 and the gear wheel 3 is no longer ensuredin the way, which is actually required.

Problems particularly occur, when the volume of a pressure chamber 14has reached its maximum value, and after passing this maximum value, thepressure chamber starts contracting. In this case it is required that aconnection exists between this pressure chamber and the outlet orlow-pressure connection. If, however, at this instant the pressurechamber is still connected with the high-pressure connection, pressuresurges occur, which have a negative effect on the operational behaviourof the machine. This is particularly the case in connection with lowspeeds. The same problem occurs, when the volume in the pressure chamber14 has passed a minimum value and starts expanding. In this case, aconnection with the high-pressure connection is required. When thispressure chamber is still connected with the low-pressure connection,there is a risk of cavitations. This means that problems always occur,when a pressure chamber assumes an extreme value of its volume.

In order to remedy these problems, the gear wheel 3 is, as shown in FIG.3, provided with recesses 20 on the sides of the teeth 21 forming theouter toothing 4. The recesses 20 are arranged approximately in theaxial centre of the gear wheel. They have an axial extension in therange from 15 to 20% of the axial length of the gear wheel 3. Theirextension in the circumferential direction will be explained inconnection with the FIGS. 4 to 7.

FIG. 4 shows a cross-section IV-IV according to FIG. 1.

FIG. 5 shows an enlarged section V according to FIG. 4.

FIG. 4 shows a situation, in which the gear wheel 3 assumes a positionin relation to the toothed ring 5, in which the upper (referring to theview in the Fig.) pressure pocket 14 has its minimum volume. As thisstate will appear for each pressure pocket, it will be sufficient toexplain the circumstances for one pressure pocket 14.

The tooth 21 of the gear wheel 3, which is in the pressure pocket,forms, together with the neighbouring rollers 7 of the toothed ring 5,substantially line-shaped contact areas 22R, 22L, in the followingcalled contact lines. In these contact lines 22R, 22L the tooth 21 andthe rollers 7 bear on each other in such a way that here the pressurechamber 14 is sealed in relation to a pressure chamber 14L on the leftside and a pressure chamber 14R on the right side.

When now the gear wheel 3 would continue to rotate, the pressure chamber14 would expand. When, at this moment, the valve arrangement 11, 12 hasnot yet established a connection with the high-pressure connection,hydraulic fluid cannot flow into the pressure chamber 14 during anexpansion. A risk of cavitations exists.

In order to counteract this risk, the two recesses 20 have a length inthe circumferential direction of the gear wheel 3, that is, they have anextension, which permits them to exceed the contact lines 22L, 22R.Thus, the recesses 20 provide a connection between the pressure chamber14 and the left pressure chamber 14L on the one side and between thepressure chamber 14 and the right pressure chamber 14R on the otherside. In this connection, the recesses 20 extend by a distance X intothe neighbouring pressure chambers 14L, 14R. Accordingly, they create a“short-circuiting” between the pressure chamber 14 and the neighbouringchambers 14L, 14R. Only a small amount of fluid is lost through thisshort-circuiting, as at this point the recess 20 is not particularlydeep. Together with the gear wheel 3 and the rollers 7 of the innertoothing 6 the recess 20 forms a throttle, whose throttling resistanceis variable. The throttling resistance has its highest value, when thepressure chamber 14 starts expanding.

However, the connection between the pressure chamber 14 and theneighbouring pressure chambers 14L, 14R created by the recesses issufficient to equalise the pressure peaks, which could occur, when thepressure chamber starts expanding. Pressure peaks here also meannegative pressure peaks.

The contact lines 22L, 22R between the tooth 21 and the rollers 7, whichoccur in the position of the gear wheel 3 in relation to the toothedring 5 shown in FIG. 4, in which position the pressure chamber 14 hasits smallest volume, determine the extension of the recesses 20 in thedirection of the tooth bottom of the gear wheel 3.

The extension of the recesses 20 in the direction of the tooth peak willbe explained on the basis of FIGS. 6 and 7.

FIG. 6 shows a view according to FIG. 3, in which the gear wheel 3 nowhas assumed a position in relation to the toothed ring 5, in which thepressure chamber 14 has its maximum volume. A further rotation of thegear wheel 3 in relation to the toothed ring 5 will force the pressurechamber to contract. When, at this instant, a connection from thispressure chamber 14 to the low pressure connection has not yet beenestablished through the valve arrangement 11, 12, impermissible pressurepeaks would occur in the pressure chamber 14, which would, in the bestcase, cause an unstable operation of the machine, in the worst case,however, damage the machine.

In order to remove or weaken these pressure peaks, the recesses 20 inthe circumferential direction of the gear wheel 3 have been made so longthat they project over the contact lines 22L, 22R of the teeth 21 withthe rollers 7 by a distance X. This again creates a short-circuitingbetween the pressure chamber 14 and the neighbouring chambers 14L, 14R,through which hydraulic fluid can escape from the pressure chamber 14,when this pressure chamber starts contracting.

A short-circuiting of this kind between a pressure chamber 14 under highpressure and neighbouring pressure chambers 14L, 14R, of which one isconnected with the low-pressure connection, is usually undesirable.When, however, this short-circuiting is dimensioned in such a way that,on the one hand, pressure peaks can be reduced, and, on the other hand,not too much fluid under high pressure is lost, the advantages of astable operation will occur, particularly with low speeds under highload, without causing a significant reduction of the volumetricefficiency.

Instead of the valve arrangement with a valve plate 11 and a channelplate 12, which bear on each other in a plane manner, it is alsopossible to use a valve arrangement, made with two rotary slides, whichare concentrically inserted in each other.

The production of a recess 20 is relatively simple. It is sufficient todive a suitable tool, for example a cutter, into the corresponding toothsides of the teeth 21. At the same time, this gives the recess 20 astraight or concavely arched bottom 23, which, in cooperation with theremaining tooth shape, ensures that from its edges the recess has acontinuously increasing depth and thus a reducing throttling resistance.

1. A hydraulic machine having a set of teeth, said hydraulic machinecomprising: a toothed ring with an inner toothing, a gear wheel with anouter toothing, the gear wheel rotating and orbiting in the toothedring, the inner toothing and the outer toothing touching each other incontact areas, thus separating pressure chambers, a valve arrangementcontrolling a connection between a connection arrangement having a highpressure connection and a low pressure connection and the pressurechambers, each contact area being provided with an opening, which, atthe time when a pressure chamber reaches an extreme value of its volume,produces a short-circuit with the neighbouring pressure chamber.
 2. Ahydraulic machine according to claim 1, wherein the opening is athrottle opening.
 3. A hydraulic machine according to claim 2, whereinthe throttle opening has a variable throttling resistance, which islargest at the moment, when the pressure chamber reaches an extremevalue of its volume.
 4. A hydraulic machine according to claim 1,wherein the opening is formed by a recess in a tooth side.
 5. Ahydraulic machine according to claim 4, wherein the recess is made inthe outer toothing.
 6. A hydraulic machine according to claim 4, whereinthe recess has a plane or concavely arched bottom.
 7. A hydraulicmachine according to claim 4, wherein the recess is arranged in theaxial centre of the toothing.
 8. A hydraulic machine according to claim4, wherein a recess is arranged on either side of a tooth.
 9. Ahydraulic machine according to claim 1, wherein the valve arrangementhas a rotatably driven valve plate, which is supported in asubstantially planar manner on a channel plate.
 10. A hydraulic machineaccording to claim 9, wherein the valve plate is loaded in the directionof the channel plate by a spring-biased balancing plate.